Tengo un ExpandableListView de elementos y en el elemento de la lista tengo TextView con dos botones para aumentar o disminuir el valor en TextView con los clics. El problema ocurre cada vez que intento desplazarme por la lista. Si incremento un elemento y luego desplazo la lista, los valores se mezclan (porque ListView sigue reciclando sus vistas) y no sé cómo solucionarlo.

He intentado muchas soulutions que he encontrado aquí, así que sí, esto puede ser un duplicado, pero no pude resolver mi problema con ningún método que he encontrado.

My ExpandableListAdapter.java

    import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.Button;
import android.widget.TextView;

import java.util.HashMap;
import java.util.List;


public class ExpandableListAdapter extends BaseExpandableListAdapter {

public static class ViewHolder {
    TextView childText;
    TextView counterText;
    Button addItemButton;
    Button deleteItemButton;

    int quantity = 0;

}


private Context context;
private List<String> listDataHeader;
private HashMap<String, List<String>> listHashMap;

public ExpandableListAdapter(Context context, List<String> listDataHeader, HashMap<String, List<String>> listHashMap) {
    this.context = context;
    this.listDataHeader = listDataHeader;
    this.listHashMap = listHashMap;
}

@Override
public int getGroupCount() {
    return listDataHeader.size();
}

@Override
public int getChildrenCount(int groupPosition) {
    return listHashMap.get(listDataHeader.get(groupPosition)).size();
}

@Override
public Object getGroup(int groupPosition) {
    return listDataHeader.get(groupPosition);
}

@Override
public Object getChild(int groupPosition, int childPosition) {
    return listHashMap.get(listDataHeader.get(groupPosition)).get(childPosition);
}

@Override
public long getGroupId(int groupPosition) {
    return groupPosition;
}

@Override
public long getChildId(int groupPosition, int childPosition) {
    return childPosition;
}

@Override
public boolean hasStableIds() {
    return false;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
    String headerTitle = (String) getGroup(groupPosition);

    if(convertView == null) {
        LayoutInflater inflater = (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_group, null);

    }
    TextView listHeader = (TextView) convertView.findViewById(R.id.list_header);
    listHeader.setTypeface(null, Typeface.BOLD);
    listHeader.setText(headerTitle);

    return convertView;
}

@Override
public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {

    final ViewHolder viewHolder;

    if(convertView == null) {
        LayoutInflater inflater = (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_item, null);

        TextView textListChild = (TextView) convertView.findViewById(R.id.list_item_header);
        TextView itemsCounter = (TextView) convertView.findViewById(R.id.items_counter);
        Button addItemButton = (Button) convertView.findViewById(R.id.plus_btn);

        viewHolder = new ViewHolder();
        viewHolder.childText = textListChild;
        viewHolder.counterText = itemsCounter;
        viewHolder.addItemButton = addItemButton;

        convertView.setTag(viewHolder);


    } else {
        viewHolder = (ViewHolder) convertView.getTag();

    }

    final String childText = (String) getChild(groupPosition, childPosition);
    viewHolder.childText.setText(childText);

    viewHolder.addItemButton.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            //int itemCount = Integer.parseInt((String)viewHolder.counterText.getText());
            //itemCount++;

            viewHolder.quantity++;
            viewHolder.counterText.setText( Integer.toString(viewHolder.quantity));

            PutOrderDrinks.addOrder(childText);

        }
    });


    return convertView;
}

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
       return true;
    } 
}